This invention relates to an electromagnetic clutch used for transmitting rotation from one, for example, a pulley rotated by an automative engine, to another, for example, a drive shaft of an automotive air conditioning compressor.
Such an electromagnetic clutch comprises a first rotary member of a magnetic material rotatable around a predetermined axis extending in a predetermined direction, a second rotary member rotatable around the predetermined axis, an armature plate facing to the first rotary member in the predetermined direction with a gap left therebetween, a plurality of leaf springs for supporting the armature plate to the second rotary member so as to make the armature plate be movable in the predetermined direction, and electromagnetic means for generating a magnetic attraction force to attract the armature plate to the first rotary member to thereby enable rotation transmission between the first and the second rotary members, as is disclosed in, for example, U.S. Pat. No. 4,227,600 (Reference 1) issued to SHIRAI and assigned to SANKYO ELECTRIC COMPANY, LIMITED, GB-A-2156013 (Reference 2) by SANDEN CORPORATION, and others.
In such electromagnetic clutches, each of the leaf springs has a particular portion which causes an elastical bending when the armature plate is moved towards the first rotary member.
However, it is disadvantageous that the electromagnetic clutches generate a relatively large noise whenever the armature plate is attracted to the first rotary member, as will later be described.